Optical image transmitting structure

ABSTRACT

An optical image transmitting device capable of transmitting an image of an object to a plurality of locations comprises a plurality of optical fibers which are bundled together at their one ends and are separated from each other at their other ends, each of the optical fibers having a refractive index distribution represented substantially by the following equation

wouvL United States 1 Kitano et a1.

OPTICAL IMAGE TRANSMITTING STRUCTURE Inventors: Ichlro Kltano,Higashinada-ku,

Kobe-shi, Hyogo-ken; Ken Koizuml, ltami-shi, Hyogo-ken; HiroyshlMatsumura, I-ligashi-ku, Osaka-shi, Osaka-fu. all of Japan Nippon SeliocKabushiki Kaisha .(a.k.a. Nippon Selioc Co., Ltd.), Tokyo-to, JapanFiled: Jan. 17, 1972 Appl. No.: 218,492

Related US. Application Data Continuation of Ser. No. 852,333, Aug. 22,I969, abandoned.

Assignee:

Foreign Application Priority Data Aug. 27, 1968 Japan 43/61371 11.5. C1.350/96 B, 350/175 GN Int. Cl. G02b 5/16 Field of Search 350/96 R, 96 B,96 WG,

Reierencea Cited UNITED STATES PATENTS 10/1971 Nishizawa et al. 350/96WG 12/1969 Hendrickaon et a1. 350/96 B X Aug. 21, 1973 3,033,123 3/1963Navias 350/115 GNX 3.320.114 5/1967 Schulz.... ..3s0/96Rx 3,434,7143/1969 M111" ..3$0/96 we OTHER PUBLICATIONS Miller, Article in BellSystem Technical Journal Vol. 44, No. 9, Nov. 1965 pgs. 2017-2030.

Kawakami et al., Article in Proceedings of the IEEE Dec. 1965, pgs. 21488t 2149.

Primary ExamineF-David H. Rubin Attorney-Robert E. Burns et a1.

[57] ABSTRACT An optical image transmitting device capable oftransmitting an image of an object to a plurality of locations comprisesa plurality of optical fibers which are bundled together at their oneends and are separated from each other at their other ends, each of theoptical fibers having a refractive index distribution representedsubstantially by the following equation where N represents therefractive index the center point thereof in a cross section of thefiber, 11 represents the refractive index at a radial distance r fromthe center point, and a is a positive constant, whereby plural images ofone object field can be respectively produced at the separated end facesof the optical fibers.

6 Claims, 5 Drawing Figures Patented Aug. 21, 1973 2 Sheets-Sheet 1 FIGfL-IJ (x 2m+3 LENGTH OF LENS( f Patented Aug. 21, 1973 3,753,607

2 She ets-Sheet 2 OPTICAL IMAGE TRANSMITTING STRUCTURE This is acontinuation of application Ser. No. 852,333 filed Aug. 22, 1969 and nowabandoned.

BACKGROUND OF THE INVENTION The present invention relates to an opticalimage transmitting device and more particularly to a device capable oftransmitting an image of an object to a plurality of different places asrespective plural images.

Heretofore, for the purpose of optical transmission of a plurality ofimages of one object to desired positions, combined use of reflectors,ordinary optical lenses, ordinary bundles of optical fibers and otheroptical elements has been necessary. However, these conventional deviceshave an inevitable drawback in that highly complex mechanisms arerequired and that they can only be fabricated at high expense.

SUMMARY OF THE INVENTION It is accordingly a principal object of thepresent invention to provide an optical image transmitting devicecapable of transmitting a plurality of images of one object to pluralseparated positions without having the above-mentioned drawbacks of theconventional devices.

The above and other objects of the invention have been effectivelyattained by a device comprising a plurality of optical fibers which arebundled at their one side ends and separated at their other ends, eachof said transmitting structure of this invention. Especially, in thecase of glass, a desired refractive index distribution can be easilyobtained by progressively varying the refractive index in the interiorof the glass by regulating the concentration of the cations composingthe forming oxides of the glass at a constant and varying theconcentration of at least two kinds of cations composing the modifyingoxides of the glass. In the case of synthetic resin, on the other hand,the required refractive index distribution can be obtained by covering aresinous core structure with several kinds of synthetic resin havingdifferent refractive indexes and capable of being mutually diffused at ahigh temperature and thereafter applying heat thereto to obtain aconsecutive variation in the refractive indexes of the resins.

The optical fibers constituting the image transmitting structure of thepresent invention function as a lens even if the refractive indexdistribution thereof roughly satisfies the above equation n N (l ar'),if not exactly. Even when terms such as r and r' are present in thebrackets in the right member of said equation, the functioning of theoptical fibers as a lens is not influ- 5 enced if their coefficients aresmall.

optical fibers having such a refractive index distribution as to nearbysatisfy the equation n N (l or), where N represents the refractive indexat center point thereof in a cross section, n represents the refractiveindex at a radial distance r from said center point, and a is a positiveconstant, whereby plural images of one object are produced at saidseparated end faces of said optical fibers by means of light projectedfrom said object placed in front of said bundled end faces of saidoptical fibers.

The foregoing and other objects as well as the characteristic featuresof the invention will become more apparent and more readilyunderstandable by the following description.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 through 4 are schematic viewsfor showing the principles of the present invention; and FIG. 5illustrates schematically an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION When a gas is flowed in a laminarflow through a pipe from one end thereof to the other end and the wallof the pipe is heated, the gas in the pipe has such a refractive indexdistribution as to be decreased nearly in proportion with the square ofa distance from a center axis of the pipe, with a result that the gashaving a refractive index distribution as described above has an imageforming capability like that of a convex lens. This phenomenon is knownas the so-called principle of a gas lens, as is described, for instance,in pp. 180 I87 of No. 3, Vol. 36, of "Oyo Butsuri (Applied Physics)."The present inventor has discovered that glass, synthetic resin andother fibrous transparent substances having the above describedrefractive index distribution can function as a lens.

Glass, synthetic resin and the like are most suitable materials of theoptical fibers constituting the image The relationship between an objectand its image according to the optical fibers constituting the imagetransmitting structure of the present invention is plotted in FIG. 1,where a fibrous lens or optical fiber I has a radius R, length r, andrefractive index distribution n N (l as), where M I.

The focal distance f of this fibrous transparent lens I can be obtainedin the same way as the analysis applied 5 to a medium having the aboverefractive index distribution which is described in pp. 465 467 of thethesis of Mr. H. Kogelnik carried in pp. 455 494 of the March, 1965,issue of the Bell System Technical Journa the U.S. technical magazine.That is, the focal distance f can be obtained according to the followingequation, when (20) C:

f= (Nc sin Ct)" However, the focal distance f is represented by adistance measured toward a space on the side of an object from a firstprincipal point of the lens or by a distance measured toward a space onthe side of an image from a second principal point. The distance I: of acorresponding principal plane H as measured inwardly from the end facesof the lens, is represented by:

h (NU' tan v. cl

In the drawing, F, and F, respectively designate the positions of focalpoints on the sides of the object and its image, while H, and H,represent, respectively, the principal planes on the sides of the objectand its image.

When an object P is placed at a distance I: from the principal plane H,of the lens I, an image Q is formed at a distance L from the principalplane H, on the side of the image of the lens. In this case, thefollowing relation k" L f is established between the distance k of theobject and the distance L of the image when it is considered withrespect to paraxial ray, in the same way as in an ordinary lens formula.

The above equations (l) and (2) representing, respectively, the focaldistance f and the principal plane distance it are shown in H0. 2 asfunctions of the length of the lens. The axis of abscissa in the graphplotted in FIG. 2 represents the length of the lens, while the axis ofordinate represents a focal distance and principal plane distance, and mrepresents a positive integer. The full lines designate the focaldistance f and the chain lines represent the principal plane distance h.The focal distance is varied within a range between (1%) and infinity,or (Nc)' and negative infinity, according to the length of the lens. Asis clear from FIG. 2, the lens has a focal point outside itself at aportion where the full line f is positioned higher than the chain lineit, that is, when the length of the lens corresponds to a value from(2c) (2m 2) to (2c) '1 (2m 1).

Light progresses through the interior of the transparent substance whileoscillating around its center axis in the shape of a sine wave havingits inherent wavelength S equal to 2 c".

When the center axis of the transparent substance is curved in part, theoptical axis, which is the oscillation center of the progressing light,is not in agreement with the center axis at the curved portion. If acertain part of the center axis is curved with a curvature radius of u,the optical axis at that part is deviated outwardly from the center axisby (2au)". As is shown in FIG. 3, the optical axis h is shifted from thecenter axis j at the curved portion of the transparent substance 2.Therefore, when (2014)" is sufficiently small as compared with theradical distance R from the center axis j to the periphery of thetransparent substance 2, the lightbeams wander around the optical axis,whereby an image is transmitted. The brightness of the image is reducedwhen (2au)' becomes larger, because the quantity of light colliding withthe side surfaces of the transparent substance is increased.Accordingly, if the transparent substance is previously curved or evenif the transparent substance is flexible and curved temporarily, thecurvature does not exceeds a certain limit, the above describedrelationship between an object and its image is kept unchanged so far asthe curvature does not exceeds a certain limit and the imagetransmission by the transparent substance is carried out. Of course, theoptical axis at the curved portion is deviated from the center axis.This state is shown in FIG. 4, where the dotted line represents theoptical axis deviated or shifted from the center axis thereof and animage of the object P is transmitted through the interior of the fibroustransparent substance 3 to form a real image Q.

However long the transparent substance may be, a light-beam which hasonce entered the transparent substance is transmitted therethroughwithout being scattered, because it is a lens system having a focaldistance f determined according to its length and principal planes H andH,

The transparent substance can be fabricated, for instance, by thefollowing process.

A bar of glass with a diameter of 1 mm and consisting of 56 wt percentof SiO,, 14 wt percent of Na,0, wt

4 percent of Tl,O and 10 wt percent of PbO was immersed in a bath ofpotassium nitrate at a temperature of 500 C for 24 hours, whereby aglass bar having a center refractive index N of 1.56, a surfacerefractive 7 -dled together at one end thereof and separated from oneanother at the other end. Referring to FIG. 5, the optical fibers 4constituting the image transmitting structure of the present inventionhave different lengths. An object field 6 to be transmitted is placed infront of one end face of the bundle of the optical fibers 4. Since theobject 6 is placed within a range of an angle of the aperturecorresponding to one end face of each optical fiber, the fibers transmitnearly the same image of the object to produce an image 5 at the otherend face thereof. The position where the image 5 is formed can beselectively adjusted either by differentiating the lengths of the fibersor by bending them. The magnitude of the image as well as selectionbetween erect and inverted images or between real and virtual images canbe obtained at will by regulating the lengths of the fibers up to thelimit of 1r C or by varying the distance between the object and thebundled end faces of the fibers.

When the position of the object 6 is brought closer to one end face ofthe optical fiber bundle, the images transmitted respectively throughthe optical fibers become somewhat different from one another and at theextreme case, when the object is brought into close contact with the endface of the bundle, the optical fibers transmit mutually differentimages each of which corresponds to that part of the object which isopposite to the end face of the respective optical fiber, wherebyentirely different images are respectively formed at other separated endfaces of the optical fibers.

We claim:

1. An optical image transmitting device comprising: means receptive of aplurality of optical images of a common object field for transmittingsame to a plurality of separate locations, said means comprising aplurality of elongated optical fibers each having two end portionsrespectively terminating in a planar end face, each of said opticalfibers having a refractive index distribution in each cross-sectionalplane in substantial accordance with the equation I: N(l-ar) wherein Nrepresents the refractive index at the center of the optical fiber, nrepresents the refractive index at a radial distance r from the centerof the optical fiber, and a is a positive constant whereby each opticalfiber has a light focusing effect, and means arranging one end portionof each of said optical fibers in a bundled together configurationwherein the planar end face of each of said one end portions ispositioned to receive one of said optical images and arranging the otherend portions of said optical fibers in transversely spaced-apartrelationship wherein the planar end face of each of said other endportions is positioned to transmit the optical image to respective onesof a plurality of separate locations and focus the transmitted opticalimage at said location; and wherein an intermediate longitudinal portionof at least some of said optical fibers extends in a curved directionwhich has a radius of curvature u selected in accordance with theexpression (2au)' R wherein R represents the radial distance from thecenter to the periphery of the optical fiber.

2. An optical image transmitting device according to claim 1; whereinsaid optical fibers are composed of a flexible material therebyrendering said optical fibers flexible.

3. An optical image transmitting device according to claim 1; wherein atleast some of said elongated optical fibers have a different length thanothers.

4. An optical image transmitting device according to claim 1; whereinall said planar end faces at the image receiving end of said bundledtogether configuration of optical fibers substantially lie in a commonplane.

5. An optical image transmitting device according to claim 4; whereinall said planar end faces at the image transmitting end of said bundledtogether configuration of optical fibers lie in mutually differentplanes.

6. An optical image transmitting device according to claim 1; includingan object field confronting the planar end faces of the bundled end ofsaid plurality of optical fibers;

a plurality of screens each positioned at one of said separate locationsin spaced confronting relationship from one of the other planar endfaces of said plurality of optical fibers for receiving thereon in afocussed condition one of the transmitted optical images.

I t i i

1. An optical image transmitting device comprising: means receptive of aplurality of optical images of a common object field for transmittingsame to a plurality of separate locations, said means comprising aplurality of elongated optical fibers each having two end portionsrespectively terminating in a planar end face, each of said opticalfibers having a refractive index distribution in each cross-sectionalplane in substantial accordance with the equation n N(1-ar2) wherein Nrepresents the refractive index at the center of the optical fiber, nrepresents the refractive index at a radial distance r from the centerof the optical fiber, and a is a positive constant whereby each opticalfiber has a light focusing effect, and means arranging one end portionof each of said optical fibers in a bundled together configurationwherein the planar end face of each of said one end portions ispositioned to receive one of said optical images and arranging the otherend portions of said optical fibers in transversely spaced-apartrelationship wherein the planar end face of each of said other endportions is positioned to transmit the optical image to respective onesof a plurality of separate locations and focus the transmitted opticalimage at said location; and wherein an intermediate longitudinal portionof at least some of said optical fibers extends in a curved directionwhich has a radius of curvature u selected in accordance with theexpression (2au) 1 < R wherein R represents the radial distance from thecenter to the periphery of the optical fiber.
 2. An optical imagetransmitting device according to claim 1; wherein said optical fibersare composed of a flexible material thereby rendering said opticalfibers flexible.
 3. An optical image transmitting device according toclaim 1; wherein at least some of said elongated optical fibers have adifferent length than others.
 4. An optical image transmitting deviceaccording to claim 1; wherein all said planar end faces at the imagereceiving end of said bundled together configuration of optical fiberssubstantially lie in a common plane.
 5. An optical image transmittingdevice according to claim 4; wherein all said planar end faces at theimage transmitting end of said bundled together configuration of opticalfibers lie in mutually different planes.
 6. An optical imagetransmitting device according to claim 1; including an object fieldconfronting the planar end faces of the bundled end of said plurality ofoptical fibers; a plurality of screens each positioned at one of saidseparate locations in spaced confronting relationship from one of theother planar end faces of said plurality of optical fibers for receivingthereon in a focussed condition one of the transmitted optical images.